Heater element



INVENTOR R. H. SINOE/V )7; 9- W ATTORNEY Patented h1g9, 1932 UNITED STATES PATENT OFFICE ROGER BULL BINDER, bl BLOOIFIELD, NEW JERSEY, ABSIGNOB TO WESTINGHOUSE nan OOIPAJI'Y, A COBPOBATI ON OF PENNSYLVANIA HEATER ELEMENT This invention relates to electron emission devices and relates more particularly to such devices in which an electron emission material is indirectly heated.

Electron emission devices such, for example, as radio tubes which operate by means of an alternating current, require a source of heat, which may be indirectly transferred to an electron emission material, to permit 1 an electron flow between electrodes in the device.

As an exam 1e of a device of this character, a radio tube esigned to operate on alternating current, such as that known in the trade 15 as the UY-227, may be considered. This tube comprises the usual bulb and base and its internal structure includes a glass press upon which the several electrodes are mounted. go Tubes of this type may employ a plate or anode, a grid or control element and a cathode assembly. The cathode assembly usually consists of a heater element such as a length of refractory wire, enclosed in a suitable insulator, which ma be quartz, procelain, thoria or a material lznown as isolantite, or other material. The heater element and the surrounding insulator may be termed a heater unit. The insulator of the heater unit is surrounded by a metallic sleeve coated with a suitable electron emitting material, as a carbonate coating, which is heated by conduction throu h the insulator from the heater element, w ich may be in the form of a filament wire, preferably of tungsten or molybdenum, but which may be of other suitable material.

In the manufacture of a thermionic device of the above character it has been the practice to provide the insulator in the form of a cylindrical member having two longitudinal bores or apertures disposed in parallel relation. A filament section of U or hairpin shape is threaded through the apertures. In order to obtain the desired heating efiiciency of the heater element it is. desirable to have the a ertures of only slightly larger diameter t an the filament. For example, the a ertures have a diameter of approximate y 6.5 to 7.5 mils when receiving a wire of about 5 mils diameter. This makes the introduct1on of the filament into the apertures a difficult and tedius operation, particularl since in the roduction of an insulator wit the double ore it often happens that the bores are not true either in diameter or with res ect to their parallel relation.

n the present invention a coiled filament 1s used in conjunction with a tubular insulator and the filament is arranged to frictionally engage the inner wall of the insulator so that the filament is self-supporting. It has been found preferable to provide a filament or heater element in the form of a double helix of a single length of wire, one end terminating in a loop and the opposite end consisting of terminals which are connected to leading in conductors of the device for the passage of electrical ener through the heater. By reason of the double coil alternating current may be employed since a non-induction winding results to the exclusion of disturbing effects as would otherwise be caused owing to the electro magnetic field. In the present form of heater the current flow in opposite directions neutralizes and makes ineffective the detrimental effects of the alternating current.

Another advantage of the present construction is that whereas the use of an insulator with a double bore requires relatively thick walls, the present form of heater makes it possible to use a comparatively thin wall insulator, whereby the heat from the heater element is more quickly conducted to the electron emission material. This is of considerable importance, particularly from the users standpoint, since ordinarily a considerable time interval is necessary after the heater is energized to put the device into operation, while with the present construction this time period is greatly reduced, both by reason of the thin wall insulator and by reason of the close relation possible between the insulator and the heater element.

It is an object of the present invention, therefore, to provide an insulator and a noninductive heating element which may be more conveniently and expeditiously assembled m quired uniformity and strength.

i The invention will be more readily understood by reference to the accompanying drawing, in which Figure 1 is a longitudinal sectional view of a cathode assembly showing a heating element therein.

Figure 2 is a transverse cross sectional view taken on line 22 of Figure 1.

The cathode assembly 5 shown in the drawing includes a filament 6 which according to the present invention is in the form of -a double helix or spiralled hairpin filament. This filament is disposed in a bore 7 of a tubular insulator 8. The coils of the filament are so arranged that portions 9 tensionally engage with the wall of the insulator thus supporting the filament. The filament may be wound so that the coils thereof are disposed in spaced relation and are of a suflicient distance apart to avoid the possibility of short circuits between the consecutive turns. The ends 10 and 11 of the filament may be connected to lead wires 12 and 13 extending from a press in the usual manner.

The insulator 8 is provided with a metallic sleeve 14 upon which a suitable electrofi emitting material such as a carbonate coatin is disposed. This coating is heated by con uction through the insulator which receives heat from the filament wire. It will be evident that this form of construction is of advantage in that it permits free thermal expansion of the filament as well as free and uniform radiation of heat from all portions of the filament surface and is, therefore, capable of long life without variation in the electrical characteristics of the device.

In applying the present double helical coil 6 to the interior of the tubular insulator 8 it has been found desirable to wind the coil on a mandrel of such size that the coil when so wound will have an outside diameter slightly less than the inside diameter of they insulator. The mandrel and coil may then he slipped into the insulator and the mandrel removed and the coil released. The coil by spirit and sec of the invention as set forth in the appen ed claims.

What is claimed is: 1. A cathode assembly for a thermionic device comprisin a tubular insulator having a relatively t in wall, an electron emission material disposed on the outer side of said insulator and a heater unit consistin of of a filament formed in a double helix having portions disposed in contact with and su ported by the lnner wall of said insulator.

n testimony whereof, I have hereunto subscribed my name this 19th da of Ma 1928.

ROGER HUL SI EN. 

